Rubber in its many forms presents many problems when it must be depolymerized, such as for the purposes of recycling.
For instance, scrap tires represent a large problem in an environmentally conscious world. In the United States and Canada alone, it is estimated that around 260 million tires are discarded annually. Clearly there is a need for a cost effective, environment preserving tire degradation process. Recycling tires is a manifold problem which includes the following factors:
1) Tires stored in dumps and landfills create general health and a hazardous waste problems. Tire dumps provide breeding grounds for pests, such as mosquitoes. Tire dump fires are extremely dangerous, they require a large amount of manpower to extinguish if indeed they can be quenched at all before burning completely. These fires also discharge toxic gas into the atmosphere.
2) The automobile tire is a complex structure consisting of not only rubber of several types, but also polyethylene pterphthalate, sulfur, polyester and fiberglass cords, steel belts and cords, copper and carbon black. Separation of these component parts presents a serious problem when recycling tires, as the component parts are of various physical and chemical character.
3) Markets must be made available for recycled materials from tires. Examples of products from recycled tires presently include: rubber crumb filler, rubber modified asphalt, and fuel chips. The steel belts and cords might also be reused by the tire manufacturers in one form or another, or otherwise be recycled as scrap metal.
Other sources of scrap rubber include industrial and laboratory waste, and waste medical supplies. Types of rubber include butadiene rubber and isoprene rubber.
At present, many tire recycling processes involve grinding up tires, or freezing the tires with liquid nitrogen before crushing and shattering them into smaller fragments. Various separation processes to remove components, such as steel fragments, are then carried out, usually by magnetic means. The rest of the particles are sieved and graded according to size, often ground to a smaller mesh, and then sold for various purposes.
Another obstacle to the efficient depolymerization of rubber is the relatively inert chemical nature of rubber itself. Rubber is generally formulated to resist environmental degradation and thus resists chemical attack designed to liberate its chemical components. Consequently, rubber has generally been disposed of by burning due to the inability to provide acceptable chemical recycling means which can proceed without the application of very strong reagents and/or large amounts of energy. Therefore it is desirable to provide a method for the efficient chemical depolymerization of rubber to render it into separate component fractions more suitable for reuse.
Yet another major hurdle to be overcome in the recycling of rubber is that presented by the wide variety of the chemical components contained in the many types of rubber, including those in vulcanized tire rubber. Such components include the polymeric components, as well as vulcanizing agents, cross-linking agents, anti-oxidants, carbon black, etc. Accordingly, it is difficult to formulate methods for depolymerizing rubber which will both be able to separate the rubber components while being able to operate in an environment of several varied chemical species, without the depolymerization reaction being adversely affected thereby, and without undesirable side reactions.
Thus it is desirable to use methods for recycling rubber which may be applied efficiently and inexpensively, and which render the rubber into useful chemical components.
The many embodiments of the present invention make progress toward the accomplishment of the above objectives and toward providing solutions to the problems discussed above. In light of the present disclosure and/or the practice of the present invention, other advantages and/or the solution to additional problems, may become apparent to one skilled in the relevant arts.